A magnetoresistor is a device whose resistance varies with a magnetic field applied to the device and is therefore useful as a magnetic field sensor. Thus, the magnetoresistor is useful as a speed or position sensor. One form of a magnetoresistor is a thin body of a high carrier mobility semiconductor material, such as indium antimonide (InSb) or indium arsenide (InAs) having contacts at its ends. However, a preferred form of a magnetoresistor is formed of a thin film of the semiconductor material and is described in detail in U.S. Pat. No. 4,926,154 (J. P. Heremans et al., issued May 15, 1990) entitled, "Indium Arsenide Magnetoresistor." This form of the magnetoresistor comprises a substrate of an insulating semiconductor material having a thin film of the magnetoresistor material on a surface thereof in the form of a narrow strip. Conductive contacts are formed at the ends of the magnetoresistor material strip.
To use the magnetoresistor as a speed or position sensor, it has been mounted in a magnetic circuit which includes a permanent magnet on which the magnetoresistor element is mounted and an exciter. The exciter is a high magnetic permeability element with a series of spaced teeth separated by slots that moves in relation to the stationary magnetoresistor element for changing the reluctance of the magnetic circuit and for causing the magnetic flux through the sensing element to vary in a fashion corresponding to the position of the teeth. The magnetoresistor element and the permanent magnet are generally formed into a single sensor package to allow for ease of mounting the package over the exciter. Referring to FIG. 1, there is shown a perspective view of a form of a magnetoresistor sensor package 10 which has been found suitable for providing a device having a high magnetic sensitivity. This sensor package and how it is used in a magnetic circuit is described in detail in U.S. Pat. No. 4,926,122 (T. Schroeder et al., issued May 15, 1990) entitled, "High Sensitivity Magnetic Circuit." The magnetoresistor sensor package 10 comprises a permanent magnet 12 having a planar surface 14 which is coated with a layer 16 of a high permeability magnetic metal, such as iron, hereinafter referred to as a ferromagnetic layer. The ferromagnetic layer 16 is covered by a layer 18 of an electrical insulating material, such as a plastic. Spaced bonding pads 20 of an electrically conductive material are on the insulating layer 18. A magnetoresistor element 22 is mounted on the insulating layer 18 between the bonding pads 20 with the contacts, not shown, of the magnetoresistor element 22 contacting and electrically connected to the bonding pads 20. Terminal wires 24 are electrically connected to the bonding pads 20 and extend from the package 10. If desired, a protective covering of an insulating material, such as a plastic, may be molded over the magnetoresistor element 22 and at least a portion of the permanent magnet 12.
Referring to FIG. 2, there is shown a magnetic circuit 25 comprising the magnetoresistor sensor package 10 of FIG. 1 and an exciter 26. The exciter 26 is a wheel having spaced teeth 28 with slots 30 therebetween. The magnetoresistor element 22 is in the form of a narrow strip mounted on the center line of the ferromagnetic layer 18 and positioned so as to be parallel to the teeth 28 and the slots 30 of the exciter wheel 26. The width of the magnetoresistor sensor element 22, as well as that of the magnet 12, are very important design parameters governing the sensitivity of the sensor and are described in detail in U.S. Pat. No. 4,926,122. The length of the magnetoresistor sensor element 22 is selected to provide a sufficiently large active surface for the required resistance and power dissipation. Theoretically, the length of the magnetoresistor element 22 is limited only by the magnet size. However, in order to minimize the influence of the magnetic end effects, the ends of the magnetoresistor element 22 are not located too close to the edges of the magnet 12.
As described in U.S. Pat. No. 4,926,122, in the operation of the magnetic circuit, the magnetic flux density distribution changes as the exciter 26 moves across the magnetoresistor sensor element 22. The magnetic flux density distribution in the magnetoresistor sensor element 22 has a peak value when a tooth 28 is aligned with the magnetoresistor sensor element 22 and a valley when a slot 30 is aligned with the magnetoresistor sensor element 22. As the exciter 26 moves, the peaks and valleys follow the exciter teeth 28 and slots 30 creating a traveling wave of flux density along the width of the sensor element 22. This yields an output from the magnetoresistor sensor element 22 which indicates position or speed. The ferromagnetic layer 16 of the package 10 serves to enhance the contrast between the peaks and valleys in the magnetic flux density distributions.
Although the magnetoresistor sensor package 10 provides a sensor having good sensitivity, it has the disadvantage that it is formed of a number of different parts and requires a number of different operations to assemble. For large-scale manufacturing operations, it would be desirable to form such a package from fewer parts which can be assembled by fewer operations. This would reduce the assembly time and the overall cost of the package.